T. LOUIS -- For the first time in more than a century, the Catholic bishops of the United States are contemplating convening a national gathering of bishops, priests, and lay people to discuss problems facing the church in this country.

The bishops, who are in St. Louis for their semiannual meeting, have set aside today for ''prayerful reflection'' on the issues that might form the agenda for such a gathering, which could be held in three years or later. And the bishops said that next June, instead of their annual spring gathering, they will hold a retreat in Denver to decide whether to go forward with the first ''plenary council'' since 1884.

The council was proposed last year by about 100 bishops, who signed petitions urging that such a gathering be held to discuss the state of the church in the wake of the sexual abuse crisis.

Although the original petitions sought discussion of issues such as ''holiness'' and were associated with the conservative wing of the church, the proposal has drawn broad interest, as well as some skepticism, because of its potentially open-ended nature.

Archbishop Daniel M. Buechlein of Indianapolis, the chairman of an ad hoc committee examining the possibility of a plenary council, said his committee has polled bishops about what they would want to discuss at such a council. In a report to the bishops conference yesterday morning, he said the bishops' top priorities for consideration, in order, are ''the identity and spiritual life of priests and bishops,'' ''the need for catechesis of the faith,'' ''the role of the laity,'' and ''concern for the decline of participation in the sacramental life of the church.''

Today, behind closed doors, the bishops plan to hear presentations on those subjects, then offer their thoughts, as they prepare to decide whether to propose the plenary council. Convening such a gathering would require approval from the Vatican. Participation is restricted by canon law, and would include priests and lay people in a limited, nonvoting role.

Bishop Richard G. Lennon, administrator of the Archdiocese of Boston, said he would support holding such a council.

''Being a history major, I'm all for it,'' he said in an interview during a morning coffee break at which he stepped onto a rainy patio to smoke a pipe. ''We had a number of them during the 19th century, and they were a wonderful exercise of church life.''

Asked what topics such a meeting should include, Lennon said: ''Catholic life -- the whole reality of how we live as Catholics. It would be a mistake to have it be one-dimensional. It's a real moment for looking to the future.''

Other key bishops also expressed support.

''This is an extraordinary moment, so to ask for an extraordinary response makes sense to me,'' Cardinal Francis E. George of Chicago said to a scrum of reporters huddled around him after a midday news conference.

Bishop Donald W. Wuerl of Pittsburgh also expressed interest in some kind of national gathering. ''At the heart of the issue is not what format we use, but that somehow this conference of bishops has to provide bishops an opportunity to get together and talk about the issues they really want to talk about, not being driven by an agenda that is already filled with committee reports and documents,'' he said.

Bishop Wilton D. Gregory, president of the US Conference of Catholic Bishops, said that among the topics the bishops will discuss today, as they contemplate the possibility of calling a plenary council, is their own credibility. ''Certainly, the teaching office of the bishop, and the credibility of leadership, will be a part of that conversation,'' he said.